This invention relates to novel flame retardant polypropylene based formulations. For the purposes of this invention "polypropylene" shall mean the isotactic homopolymer formed from propylene or the block copolymer of such isotactic homopolymer and polyethylene. The block copolymer will generally contain up to 94% homopolypropylene segments. Such homopolymers and block copolymers are well-known to those skilled in the art.
Polypropylene based formulations have proven to be commercially important for use in the production of film, injection and blow molded articles, extruded pipe, wire insulation and fibers. For many of these uses, it is important that the resultant film, articles, pipe, etc. have a flame retardant quality.
Flame retardancy can be obtained by including a flame retardant compound and an inert filler in the formulation. The flame retardant compound is generally a brominated hydrocarbon which can be used alone or with a synergist, such as Sb.sub.2 O.sub.3. The inert filler can be talc, mica, silica, clay, chalk, etc. so long as the filler is inert to the formulation and not a ready fuel source. While such formulations may be useful, they are not ideal, since, to obtain a UL-94 rating of V-0, the amount of flame retardant and the amount of inert filler used in the formulation is generally high, e.g. about 25 wt. % flame retardant, 10 wt. % Sb.sub.2 O.sub.3 and about 15 wt. % inert filler, based upon the total weight of the formulation. The high amount of flame retardant adds to the expense of the formulation while the high amount of filler adversely affects some of the physical properties of articles produced from the formulation. For example, the stiffness of the molded article is greatly increased, while its surface gloss is decreased when high amounts of inert filler are present.
There are some brominated hydrocarbon flame retardants which can provide the flame retardant quality needed without either the use of high amounts of flame retardant or inert filler in the formulation, e.g. tetrabromobisphenol-A bis(2,3-dibromopropylether). Such flame retardants, however, are generally expensive.
It is therefore an object of this invention to provide economical flame retardant polypropylene based formulations which do not require high amounts of flame retardant and/or inert filler. It is another object of this invention to provide articles molded from such formulations.